Will a Merc 120 stay running if battery disconnected?

[egleas84]

Trying to determine if my battery is bad or alternator is bad. With the engine running if I pop the terminals off the battery the engine kills. I test 12v at the batt, alt and my isolator.

 

[egleas84]

Re: Will a Merc 120 stay running if battery disconnected?

More background: ran it full open on a lake earlier today then idled for awhile with the blower running shutoff to drift for awhile. Wouldnt turn over after that. Batt charged 2 days ago.

 

[achris]

Re: Will a Merc 120 stay running if battery disconnected?

Don't EVER run the engine with no battery connected, good or bad! The alternator needs to see a reference or the voltage will go through the roof, and destroy instruments and accessories.

Take the battery to a battery shop and have them load test it....

Chris.......

 

[egleas84]

Re: Will a Merc 120 stay running if battery disconnected?

Don't EVER run the engine with no battery connected, good or bad! The alternator needs to see a reference or the voltage will go through the roof, and destroy instruments and accessories.

Take the battery to a battery shop and have them load test it....

Chris.......

Well I'll never to do that again.

 

[Bt Doctur]

Re: Will a Merc 120 stay running if battery disconnected?

A quick test is to turn the key to on and look at the voltage eg. 11.Start the engine, voltage should be higher than starting voltage.If no dash voltmeter, hook a voltmeter directly to the battery terninals.
A second test of the isolator is necessary , may have blown a diode and no power is going thru it.

 

[egleas84]

Re: Will a Merc 120 stay running if battery disconnected?

A quick test is to turn the key to on and look at the voltage eg. 11.Start the engine, voltage should be higher than starting voltage.If no dash voltmeter, hook a voltmeter directly to the battery terninals.
A second test of the isolator is necessary , may have blown a diode and no power is going thru it.

I think you're right about the isolator come to think of it. I went all over with my digital multimeter earlier....
Engine off everything was 12V
Acc on and engine off it was less than 12V
Engine on at alt was 13.8 V
Engine on at bat was 12V
Engine on at bat w/acc on was less than 12V at batt.
Voltmeter in instrument cluster always reads 10V with key on engine on or off... (faulty for sure)

Sounds about right to me! I'll bypass the isolater and test at the batt again and should see the 13.8 with engine running, right?

 

[egleas84]

Re: Will a Merc 120 stay running if battery disconnected?

I think you're right about the isolator come to think of it. I went all over with my digital multimeter earlier....
Engine off everything was 12V
Acc on and engine off it was less than 12V
Engine on at alt was 13.8 V
Engine on at bat was 12V
Engine on at bat w/acc on was less than 12V at batt.
Voltmeter in instrument cluster always reads 10V with key on engine on or off... (faulty for sure)

Sounds about right to me! I'll bypass the isolater and test at the batt again and should see the 13.8 with engine running, right?

Bypassed isolator. Checks out now. Gauge on dash even reads 12V . Thanks!